Pulling out steel sheet pile often harmfully deforms neighboring ground because of adhesion and skin friction between the pile and the ground. Steel H piles used in soil cement retaining walls could hinder additional construction and therefore should be removed. However, they usually are not removed due to high adhesion. To solve these problems, we developed new paint and sheet absorbent polymer materials for reducing the adhesion and skin friction. The performance of the materials was discussed and the effectiveness was confirmed through a series of laboratory tests and field tests.

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 Generally it is thought that occurrence of excess pore water pressure in liquefied ground leads to the loss of shear strength and shear modulus and dissipati on of excess pore water pressure recovers the state of the liquefied ground compared with the ground before liquefaction occurred by earthquake. Therefore, it is rare to report results of investigation to compare the states of the ground before and after liquefaction systematically. In this study, full-scale field experiment by using controlled blast technique was carried out to assess the behavior during and after liquefaction and densification of liquefied ground. This paper describes the distribution of volumetric strain, recovery and increase in N-value and time history of densification and N-value of liquefied layer through the observational results which were obtained by some kinds of sounding tests before and after liquefaction.

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 Japan is vulnerable to landslide disasters caused by heavy rainfall. The most common type of landslide disasters is slope failure. In order to mitigate slope failure disasters, a real-time forecasting system using short-term rainfall prediction information is needed. One of the key factors of slope failure is the ground water level. Therefore it is important to determine the ground water level in the surface soil layer in order to carry out a risk assessment. The most important of risk assessment is to evaluate the potential of slope failure quickly, in order to provide advance warning and enable local residence to be evacuated in good time. In this respect, an accurate analysis of the data, together with a simulation of the behaviour of ground water in the surface soil layer, will help to assess the potential for slope failure.
 The ground water level estimation model, using the relationship between the ground water level and surface soil layer (H/D-S_r) is proposed as a model which can be analyzed in a short period of time. In this model, both rainfall infiltration and the seepage processe s are simplified by using this relationship. In this paper, the authors propose to modify this model in order to improve estimation accuracy. In addition, field reliability of the proposal model is verified by comparing it with the results of the saturated - unsaturated flow analysis (FEM). As a result, its effectiveness is confirmed.

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 In safety assessments of radioactive waste disposal facilities, ground water flow analysis are used for calculating the radionuclide transport pathway and the infiltration flow rate of groundwater into the disposal facilities. For this type of calculations, the mixed hybrid finite element method has been used and discussed about the accuracy of ones in Europe. This paper puts great emphasis on the infiltration flow rate of groundwater into the disposal facilities, and describes the accuracy of results obtained from mixed hybrid finite element method by comparing of local water mass conservation and the reliability of the element breakdown numbers among the mixed hybrid finite element method, finite volume method and nondegenerated finite element method.

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 The back-filling improves the stability of a caisson used for breakwater against wave force. But, the extent of the improvement of the stability is affected by the interaction among the back-filling and the caisson and the foundation. A series of the model loading experiments was carried out to clarify the effects of the interaction to the stability. In this series of experiments, horizontal static load was applied to the model caisson having back-filling. Sliding failure surface was estimated from the deformation of rubble mound and back-filling. Passive earth pressure by back-filling calculated by wedge theory was compared with the experimental results. New stability evaluation method considering circular arc failure mode was developed and evaluated its validity. Followings are main conclusions in this research; 1) Increment of stability of a caisson against wave force can be estimated from wedge theory. 2) Both sliding and bearing capacity stability were considered in one time using newly developed evaluation method considering circular arc failure mode.

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 In order to examine the mechanism of unsaturated sandy slope due to rainfall infiltration, suction unloading test and absorbing tests under anisotropic stress condition are implemented for sandy specimens. Water increasing ratio during each absorbing st ep of absorbing test is different from that of suction unloading test. Deviator and volumetric strain increasing rate at each absorbing step are almost linear with water content increasing rate at the step. Moreover, they have clear correlation with suction-stress increment rate at the step. It suggests that strain increment during absorbing process has unique relation with net principal stress increment corr ected with suction-stress during the process.

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 So far, authors have proposed a method to improve earthquake resistance of pile foundations by partially solidifying an underground part of the pile foundations, and the effect of reinforcement has been confirmed by shaking table tests and the lateral loading tests of a full scale model. Though the solidified body is usually designed as an elastic body, it is possible to design the body considering the damage by the tensile stress when a seismic ground motion is assumed to be level 2. Therefore, material tests of the solidified body for the cohesive soil were executed, and the characteristics of the tension softening and the cyclic deformation behavior of the solidified bod y were clarified. Moreover, loading tests that used wall models of the solidified body were executed, and the effects of the shape on the tension softening and the cyclic deformation behavior of the solidified body were clarified. In addition, a numerical simulation by elastoplastic FEM analysis that considers the damage of the solidified body was executed, and the tension softening and the cyclic deformation behavior of the solidified body were reproduced.

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 In the current concept of repository for radioactive waste disposal, compacted bentonite as well as bentonite-based material will be used as an engineered barrier mainly for inhibiting migration of radioactive nuclides. In most cases, swelling pressure is one of the most important characteristics of bentonite as an engineered barrier. However measured swelling pressure by laboratory tests often varies considerably even if index parameter, such as eff ective clay density, is constant. Thus, existing study already revealed that difference among swelling pressure test apparatuses was the most influencing factor. In this study, swelling model of unsaturated bentonite is proposed for simulating the effects of three test conditions, which are deformability of swelling pressure test apparatuses, height of specimens and initial water content, on measured swelling pressure. Consequently, it is revealed that the effects of three test conditions on swelling pressures can be simulated by the model and that scattering of measured swelling pressure is mostly attributable to deformability of swelling pressure test apparatuses and height of specimens.

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 In this paper, the effects of moulding water content and compaction method on strength and deformation properties were evaluated by means of consolidated undrained triaxial compression test and bender element test on a silty sand. The test results showed that the specimens compacted at water content being slightly dry side of the optimum water content exhibited the lowest compressibility and the highest peak deviator stress. Effects of compaction method were manifested in that the peak deviator stress of a statically compacted specimen was hi gher than the dynamically compacted specimen. These test results were interpreted by considering the soil structure of compacted soil by bender element test.

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 Steel sheet pipe pile foundations with large diameter steel pipe sheet pile were used for the foundation of the main pier of the Tokyo Gateway bridge. However, as for the large diameter steel pipe pile, the bearing mechanism including a pile tip plugging effect is still unclear due to lack of the practical examinations even though loading tests are performed on Trans-Tokyo Bay Highway.
 In the light of the foregoing problems, static pile loading tests both vertical and horizontal directions, a dynamic loading test, and cone penetration tests we re conducted for determining proper design parameters of the ground for the foundations. Design parameters were determined rationally based on the tests results. Rational design verification was obtained from this research.

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 Ground anchors (hereinafter anchors) are important to do the maintenance after construction. Residual tensile strength of anchors are generally confirmed by lift-off test that pulls an anchor using a hydraulic jack. However, the lift-off test has not been established a proper testing method. Therefore, it may not have been proper maintenance from measurement variability.
 In this paper, we conducted various lift-off test at cut slope of the expressway, and made proposals on proper lift-off test method.

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 Japan Atomic Energy Agency has been conducting the Horonobe Underground Research Laboratory (URL) project in Horonobe, Hokkaido, as a part of the research and development program on geological disposal of high-level radioactive waste. Pore water pressure and water content around a horizontal drift in the URL have been monitored for over 18 months since before the drift excavation was started. During the drift excavation, both pore water pressure and water content were decreasing. Pore water pressure has been still positive though it continued to decrease with its gradient gradually smaller after excavation, while water content turned to increase about 6 months after the completion of the excavation. It turned to fall again about 5 months later. An unsaturated zone containing gases which were dissolved in groundwater may have been formed around the horizontal drift.

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